Seven species of fishes, Catostomus commersonii (Lacépède), Etheostoma nigrum Rafinesque, Micropterus dolomieu Lacépède, Notemigonus crysoleucas (Mitchill), Notropis hudsonius (Clinton), Perca flavescens (Mitchill), and Percina caprodes (Rafinesque) from the St. Lawrence River, Quebec, Canada, were found infected with progenetic specimens of Neochasmus spp. in the orbits and/or the body musculature. Worms displayed varying degrees of maturation. Eggs occupied the entirety of the worm in late stages of development and persisted as distinct clusters in situ after worm death. Populations of parasites were studied monthly in E. nigrum from one site between May and October in order to follow parasite recruitment, development and maturation. Recruitment of parasites was observed in young-of-the-year fish primarily in July and continued through October. Worms matured rapidly, displaying egg production within a month. Later developmental stages, in which eggs occupied most of the worm, and clusters of eggs became abundant by September. Infections in overwintered fish collected in May consisted mainly of worms in early stages of egg production and of clusters of eggs. When hatched artificially, eggs from the clusters released viable miracidia, indicating that they survive beyond the lifespan of the adult worm. It is suggested that progenesis is a fixed characteristic of the life cycle of these species, that egg dispersal requires the death of the host and that it is facilitated by predation. All prior records of Neochasmus spp. are examined, leading us to conclude that the role of the putative definitive host (primarily basses) has been reduced to that of a dispersal agent. Current hypotheses concerning the evolution and maintenance of progenesis are considered, but it is concluded that they do not apply to this host-parasite system.
Anguillicola australiensis (Johnston et Mawson, 1940) is widespread and common in Anguilla reinhardtii Steidachner in rivers and dams of eastern Queensland, Australia, having been found in nine out of ten localities. Overall prevalence was 50% and maximum local prevalence reached 77.7%. The parasite never attained high levels of abundance and maximum adult abundance never exceeded 3.22 or intensity 10. Adults were overdispersed throughout the eel populations and abundance was unrelated to eel or swimbladder size. The greater part of the adult population was composed of immature parasites. The occurrence of larvae in the swimbladder wall was erratic and unrelated to the size of the adult population. Larvae were never abundant and the great majority were damaged by a host response. It appears that parasites either pass through the swimbladder wall rapidly and moult to adults or if delayed are destroyed. There was no indication that a paratenic host was involved in the life cycle. There was no evidence that adult parasites had any local pathogenic effects on their hosts. The population biology of Anguillicola australiensis in its natural host Anguilla reinhardtii appears to be far more similar to those of other Pacific species of Anguillicola in Anguilla japonica in China and Japan than to A. crassus in Anguilla anguilla in Europe or Japan. This latter host-parasite combination appears to be the exception not the rule. It is suggested that the lack of pathogenicity of A. australiensis may reflect a long period of host-parasite co-evolution and/or lower transmission rates resulting in lower parasite population densities.
Over the last decade there has been a tremendous increase in the use of flow cytometry (FCM) in studies on the biosystematics, ecology and population biology of vascular plants. Most studies, however, address questions related to differences in genome copy number, while the value of FCM for studying homoploid plant groups has long been underestimated. This review summarizes recent advances in taxonomic and ecological research on homoploid plants that were made using FCM. A fairly constant amount of nuclear DNA within each evolutionary entity together with the often large differences between species means that genome size is a useful character for taxonomic decision-making. Regardless of the number of chromosomes, genome size can be used to delimit taxa at various taxonomic levels, resolve complex low-level taxonomies, assess the frequency of interspecific hybridization or infer evolutionary relationships in homoploid plant groups. In plant ecology and evolutionary biology, variation in genome size has been used for prediction purposes because genome size is associated with several phenotypic, physiological and/or ecological characteristics. It is likely that in the future the use ofFCM in studies on taxonomy, ecology and population biology of homoploid plants will increase both in scope and frequency. Flow cytometry alone, but especially in combination with other molecular and phenotypic approaches, promises advances in our understanding of the functional significance of variation in genome size in homoploid plants.
Integrated Population Modelling (IPMs) is a computational method for estimating population and demographic parameters that can improve precision relative to traditional methods. Here we compare the precision of IPM to traditional mark-recapture analysis to estimate population parameters in the common dormouse (Muscardinus avellanarius). This species is relatively rare across its European range and field estimation of demographic parameters can be challenging, as several parts of the life history are difficult to observe in the field. We develop an IPM model incorporating dormouse nest counts and offspring counts, which is data often recorded as a standard part of dormouse nest box monitoring. We found a significant improvement in precision in the estimation of demographic parameters using IPM compared to standard mark-recapture estimation. We discuss our results in the context of common dormouse conservation monitoring.